DNA polymerase I of E. coli is an enzyme that appears to play an essential role in the cell both during replication, in the processing of Okazaki fragments, and in repair of damaged DNA. The recent cloning of its structural gene, polA, into the genome of bacteriophage lambda has made possible a detailed analysis of DNA polymerase I by facilitating structural studies both of the protein and of its gene. In this proposal we outline experiments for determining the nucleotide sequence of the polA gene (and thereby the amino acid sequence of the protein) and the regions controlling its expression. The polA transcriptional promoter will be defined and characterized and methods for obtaining regulatory mutants are suggested. The lambda polA phage also provides a means for fine structure analysis of the polA gene. Some polA mutations inactivate certain enzymatic functions of DNA polymerase I while leaving others intact. We propose to use the cloned gene both to map and eventually to sequence these polA alleles.